Cesium calix arenes

Calixarene crown-6 compounds, which are neutral extractants like crown ethers, are able to coextract technetium with cesium. Tests carried out with several calix-arene-crown ethers (MC7, MC8, MC14, BC2, BC5, BC8, and BC10) show that the extraction of technetium, present in the aqueous phase at a concentration 10 5 M, is enhanced as the cesium concentration in the aqueous phase increases from 10 5 to 10-2 M. As expected, an increase of nitrate concentration prevents pertechnetate extraction in competition with nitrate anion. The extraction of technetium is only appreciable when the nitric acid does not exceed 1 M. Distribution ratios DCs (close to 8) are comparable for the various calixarenes. However, a decrease of extraction is observed for naphtho derivatives.88 89... 

Meier. U.C. Detellier. C. Mechanisms of formation and dissociation of a cesium-calix[4]arene acetamide complex in solution A Cs-133 dynamic NMR study. J. Phys. 

Other recent works in this field, studies on the transport of alkali and alkaline earth cations with p-zerr-butyl calix[n]arene esters and amides, were carried out by Arnaud-Neu et al. [20] and Casnati et al. [21]. They prepared 1,3-alternate calix[4]arene-crown-6 as a new class of cesium selective ionophore. 

Sachleben, R. A., Bonnesen, F. V., Descazeaud, T., Haverlock, T. J., Urvoas, A., Moyer, B. A., Surveying the extraction of cesium nitrate by 1,3-alternate calix 4-arene crown-6 ethers in 1,2-dichloroethane, Solv. Extr. Ion Exch., 17,1445-1459, 1999. 

Thuery, P., Nierlich, M., Bryan, J.C. et al. 1997. Crown ether conformations in 1,3-calix[4]arene bis(crown ether) Crystal structures of a cesium complex and solvent adducts and molecular dynamics simulations. J. Chem. Soc. Dalton Trans. 1997 (22) 4191 4202. 

Dozol, J.-F., Lamare, V., Simon, N., Ungaro, R., Casnati, A. 2000. Extraction of cesium by calix[4]arene-crown-6 From synthesis to process. In Calixarene for Separations. Lumetta, G.J., Rogers, R.D., Gopalan, A.S. Eds. ACS Symposium Series No. 757, American Chemical Society, Washington, DC, pp. 12-25. 

Engle, N.L., Bonnesen, P.V., Tomkins, B.A., Haverlock, T.J., Moyer, B.A. 2004. Synthesis and properties of calix[4]arene-bis[4-(2-ethylhexyl)benzo-crown-6], a cesium extractant with improved solubility. Solvent Extr. Ion Exch. 22 (4) 611-636. 

Harmon, B.W., Ensor, D.D., Delmau, L.H., Moyer B.A. 2007. Extraction of cesium by a calix[4]arene-crown-6 ether bearing a pendant amine group. Solvent Extr. Ion Exch. 25 (3) 373-388. 

In the second project, gathering nine teams from six EC countries, more than 150 new extractants were prepared and studied, and the target was reached for the decategorization of waste. Dialkoxy calix[4]arene-crown-6 for cesium, octaamide calix[8] arenes, and CMPO-like calixarenes for actinides display much higher complexing and extracting abilities than other classical extractants, crown ethers, or dicarbollides proposed and sometimes used for this purpose. 

Most of the studies carried out on cesium extraction conclude that the most efficient crown ethers for extraction of this cation are benzo-21-crown-7 derivatives. Like dicarbollides, these compounds need a synergistic agent or polar diluent modifier to allow cesium to be extracted from very acidic solutions. The resulting selectivity for cesium over sodium is low. Only dialkoxy-calix[4]arene-crown-6 and calix[4]arene bis(crown-6) compounds allow objectives to be fulfilled extraction of cesium at low-level concentration from acidic media.19... 

In 1982, /Mert-butyl-cal i x n larenes were studied by Izatt et al. for their capacity to transport cesium from an alkaline medium ([MOH] = 1M) through bulk liquid membranes made of a mixture of diluents able to dissolve these compounds methylene chloride, carbon tetrachloride, and dichloromethane. Experiments were carried out using p-tert-calix[8]arene to measure the rate of cesium transport under conditions of varying source pH. The values of the transport rate, small below a pH of 12, rise rapidly beyond this value, hence confirming that a proton is removed from the ligand in the complexation process. Under such conditions, tetramer, hexamer, and octamer (n = 4, 6, and 8, respectively) display a high selectivity for cesium over the other... 

The significant selectivity for cesium over rubidium (,S Cs/Rb = 39), compared with that obtained for the calix[4]arene-crown-6 derivatives (8 for MC8 and less than 5 for MC14), has to be pointed out. Replacement of 0.1 M of sodium hydroxide by potassium hydroxide strongly decreases the cesium distribution ratios for calix[4] arenes-crown-6 (DCs < 1). On the contrary, they are slightly increased for tBuC[4], leading to a cesium-over-rubidium selectivity exceeding 150. This selectivity value... 

The cation-7t interactions were evidenced by Prodi, who studied the photophysical properties of calix[4]arene-crown and their complexes with alkali metal ions. The presence of these cation ions usually caused weak effects on the absorption spectra, but sometimes caused marked changes in the intensity and wavelength maxima of the fluorescence bands of the calixarenes. The fluorescence quantum yields of complexes with alkali metal follows a precise trend for both MC46 and MC7, decreasing from potassium to cesium. These changes were explained by cation-Tt interactions between the metal ion and the two aromatic rings pointing toward it.30... 

The first studies performed at Strasbourg University by the picrate extraction method developed by Pedersen reveals a high preference of calix-crowns fixed in the 1,3-alternate conformation for cesium. In contrast to its conformational isomer, di-isopropoxy-calix[4]arene-crown-6 in the cone conformation does not extract cesium (Table 4.4). 

Electrospray Ionization/Mass Spectrometry (ES/MS), a soft-ionization desorption technique using polar solvents such as water, methanol, or acetonitrile, was used for direct measurement of cations in solution. The first measurements carried out with mono or bis(crown-6) calix[4]arenes from an equimolar cation-extractant solution confirm that the calixarenes mono(crown-6) extract only one cesium cation. On the contrary, in the same conditions, bis(crown-6) calix[4]arenes can extract two cesium cations for a ratio Cs/BC6 equal to 2.5. The binuclear complex (composed of two cesium cations) is the major species. Cesium/sodium selectivity measurements implementing various mono or bis(crown-6) calix[4]arenes were in agreement with liquid/liquid results.42... 

MD simulations performed on calix[4]arene-monocrown-6 and on calix[4]arene-bis-crown-6 and their alkali complexes, suggested that incorporation of aromatic groups in the crown ether loop was a possible way to enhance cation binding and cesium over sodium selectivity.45... 

For the calix[4]arene-bis(crown-6), the trends are the same on adding a benzo (BC5) or a naphtho group (BC10) in improving the extraction efficiency and the selectivity for cesium over sodium. However, the distribution ratios, although higher... 

In water, the introduction of a counteranion (NOy) induces a stronger electrostatic interaction, which tends to draw the cations out of the mean plane of the crown ether loop. Simulations with cesium nitrate and the various calix[4]arene-biscrowns show that the best fit is obtained with BC8 and BC9.59... 

Sachleben et al. observed that for bis(alkoxy)calix[4]arene monocrown ethers, reducing the size of the alkoxy substituent from octyl to allyl increased the cesium extraction by 10%-30% and the cesium-to-potassium selectivity by 20%-40%, with little impact on cesium over sodium selectivity. A standard modeling approach was used to analyze the complementarity of the calix-crown cavity toward potassium and cesium. MM3 optimizations were performed by modifying the K+ and Cs+ complexes, replacing the 1,3-dioxybenzene-substituent with tert-butoxy, methoxy, or hydrogen groups. 

In conclusion, calix[4]arene-bis(crown-6) and dialkoxy calix[4]arene crown-6, and especially their dibenzo derivatives, which display an important hydrophobic-ity, seem best suited for the extraction of cesium from very acidic media or media containing large amounts of sodium. In 2006, Mohapatra confirmed the high efficiency and selectivity of BC5 and BC10 for the extraction of cesium from simulated acidic high-activity level waste. The Cs distribution ratio follows the trend of diluent... 

To verify that carriers were not leaching from the membrane, cesium fluxes were measured for 24 h with diisopropoxy calix[4]arene crown-6 and di-NPOE calix[4] arene crown-6 (for this calixarene, the alkoxy group is replaced by a NPOE moiety) as carriers, after which both the source phase and the receiving phase were replaced. The cesium flux remained constant even after three replacements thus it, was concluded that the carriers are not leaching from the membrane (Table 4.13).79... 

Here, P s and /<. s are the cesium permeability in the ith transport experiment and in the first run, respectively, and R = (Vfeed+ Vslnp)/VSLM, Vfeed, Vstrip, and VSLM are the volumes of feed and stripping aqueous phases and the volume of organic phase in the membrane, respectively. Kp is the apparent partition constant of the carrier between the SLM and both aqueous and stripping solutions. Values of this apparent partition constant can be deduced via linear regression of log PCs versus (i-1). They are equal to 128,100, 29,100, 106,700, and 295,000, respectively, for decyl-benzo-21-crown-7, calix[4]arene-bis(crown-6), calix[4]arene-bis(benzo-crown-6), and calix[4]arene-bis(naphtho-crown-6). Calix[4]arene-bis(crown-6) rapidly leaked off the membrane... 

Distribution ratios and transport were carried out on real HAW arising from dissolution of a mixed oxide of uranium and plutonium (MOX) fuel (burnup 34,650 MW d/tU), where uranium and plutonium have been previously extracted by TBP.86 The experiments were performed in the CARMEN hot cell of CEA Fontenay aux Roses with two dialkoxy-calix[4]arene-crown-6 derivatives (diisopropoxy and dini-trophenyl-octyloxy). High cesium distribution ratios were obtained (higher than 50) by contacting the HAW solution with diisopropoxy calix[4]arene-crown-6 (0.1 M in NPHE). Moreover, the high selectivity observed with the simulated waste was confirmed for most of the elements and radionuclides (actinides or fission products Eu, Sb, Ce, Mo, Zr, and Nd). The residual concentration or activity of elements, other than cesium, was less than 1% in the stripping solution, except for iron (2%) and ruthenium (8%) the extraction of these two cations, probably under a complexed... 

---